Original User: Hornbydd
OK a couple of other things to check:
Your flow direction grid, is it valid and for the area? When I say valid it has only the values of 1,2,4,8,16,32,64 & 128?
Do you have a pre-existing Processing Extent set which may be for some other region? You access that via the spatial analyst toolbar > options.
Finally if you are using the raster calculator from the spatial analyst toolbar have you tried the expressions
FLD = FlowLength([flowdir_fill5],"#","DOWNSTREAM")
FLU = FlowLength([flowdir_fill5],"#","UPSTREAM")
The expression for a raster calculator is flow direction grid, weight grid, keyword. So the "#" just means default as this is an optional parameter.
Duncan